1. Field of the Invention
The present invention relates to a vehicle wheel.
2. Description of the Related Art
One-piece type wheels which are integrally formed by casting, two-piece type wheels having a construction that is split into a rim member and a disk member, and three-piece type wheels having a construction that is split into an inner-rim member, an outer-rim member and a disk member, are widely used as vehicle wheels that comprise light alloys such as aluminum alloys and the like.
Where two-piece type wheels and three-piece type wheels are concerned, wheels in which the disk member is manufactured by casting or forging and the rim member is constructed from a rolled material that is superior in terms of processing characteristics and brightness have been put to practical use. Rim members used include members for which a plate-like rolled material is rolled up to form a tube and both ends of this material are welded together, whereupon the member is molded into the desired shape by spinning, as well as members for which a disk-like rolled material is molded into a cylindrical shape with a bottom, whereupon the bottom is cut away to make a tubular molding which is molded into the desired shape by spinning, before being polished and subjected to a surface treatment.
Further, one-piece type wheels are superior in terms of mass production characteristics. However, the mold used is large and complex so that molds are required for each size, and hence the cost of manufacturing the wheel is high. Accordingly, when production numbers are small, It is preferable to split the construction into two pieces or three pieces and to manufacture the disk member alone by casting or forging. Furthermore, where two-piece or three-piece type wheels are concerned, the outer-rim part can be constructed from a rolled material with a fine texture. The design face side of the outer-rim part can therefore be formed having a lustrous surface, whereby the design characteristics of the wheel can be improved.
However, where three-piece type wheels are concerned, the number of parts is higher and there is a corresponding increase in the manufacturing costs. With two-piece type wheels, although there are fewer parts, there is the problem that because the disk member is disposed on the inside of the rim member, the mechanical strength of the wheel drops due to thermal degradation of the welded section in which these members are directly welded together.
Accordingly, a vehicle wheel like the aluminum vehicle wheel disclosed in Japanese Utility Model Laid-Open Application No. 58-54303 has also been proposed, this wheel being a vehicle wheel with a construction that is split into an outer-rim member which constitutes an outer-rim part, and a wheel-constituting member comprising an integral molding that constitutes an inner-rim part and a disk part, wherein an annular fastening part which extends inward is formed on the outer-rim member end portion on the attachment face side, and an assembly face which is oriented perpendicular to the axial center is formed on the circumferential portion of the wheel-constituting member on the design face side thereof so that the fastening part of the outer-rim member overlaps the assembly face of the wheel-constituting member and the fastening part and the assembly face are integrally joined by means of a plurality of nuts and bolts which are disposed at intervals in the circumferential direction.
This wheel is such that the outer-rim member can be manufactured easily and inexpensively from a rolled material or the like, and the wheel-constituting member that constitutes the inner-rim part and disk part can be manufactured by casting or forging. Although a large mold must be used in comparison to a case where the disk member alone is manufactured by casting or forging as is true for two-piece and three-piece type wheels and so forth, the wheel can be manufactured using a mold that is smaller and less expensive than that used for a one-piece type wheel which is manufactured by casting of the entire wheel. Furthermore, there are fewer parts than for a three-piece type wheel, and therefore this wheel can be manufactured at a lower cost than a three-piece type wheel. Furthermore, the outer-rim member is constructed from a rolled material with a fine texture, meaning that a lustrous ornamental surface with superior design characteristics can be formed on the outer-rim part on the design face side thereof in the same manner as for two-piece type and three-piece type wheels.
However, the vehicle wheel above has been confronted by the problem that because the outer-rim member and the wheel-constituting member are joined to one another by means of a plurality of nuts and bolts which are disposed at fixed intervals in a circumferential direction, there is a larger number of parts and manufacturing costs are higher, and it takes a long time to tighten the bolts, which results is a corresponding decline in producibility.